Browsing by Author "WU, JS"

Now showing 1 - 20 of 35

A NOVEL TECHNIQUE FOR LOW-THRESHOLD AND HIGH-POWER INGAAS/GAAS STRAINED-LAYER 0.98-MU-M BURIED HETEROSTRUCTURE LASER FABRICATION
(1992-02-01)
LIOU, DC
;
CHIANG, WH
;
LEE, CP
;
CHANG, KH
;
LIU, DG
A novel fabrication technique has been developed for InGaAs/GaAs strained-layer buried heterostructure lasers. Dielectric masks and Zn diffusion are not required in this technique. This novel fabrication process is much easier than the conventional approach and yields excellent laser results. A low threshold of 3 mA and high-power operation for lasing wavelength of 9800 +/- 20 angstrom have been achieved with graded index separate confinement heterostructure devices using this novel technique.
AN ALGORITHM FOR COMPUTING THE RELIABILITY OF WEIGHTED-K-OUT-OF-N SYSTEMS
(1994-06-01)
WU, JS
;
CHEN, RJ
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
This paper constructs a new k-out-of-n model, viz, a weighted-k-out-of-n system, and proposes an O(n . k) algorithm for computing its reliability.
AN O(KN) ALGORITHM FOR A CIRCULAR CONSECUTIVE-K-OUT-OF-N-F SYSTEM
(1992-06-01)
WU, JS
;
CHEN, RJ
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
An O(k.n) algorithm is described for evaluating the reliability of a circular consecutive-k-out-of-n:F system.
AUTOMATIC CONSISTENCY VERIFICATION OF MECHANICAL CAD FILES
(1993-07-01)
PERNG, DB
;
CHEN, Z
;
WU, JS
;
資訊科學與工程研究所
;
工業工程與管理學系
A system for automatic verification of the exactness of the CAD files of a mechanical part with planar and cylindrical faces through 3D part reconstruction is described. A set of consistency checking rules are specified to facilitate the part reconstruction. The system not only reconstructs the 3D geometry from a correct drawing file, but also produces adequate error messages to aid the designer to make corrections. We shall present our method with illustrations. Experimental results indicate that the set of checking rules is very useful and the system is very effective.
BEHAVIOR OF THE 1ST LAYER GROWTH IN GAAS MOLECULAR-BEAM EPITAXY
(1990-10-01)
LIU, DG
;
LEE, CP
;
CHANG, KH
;
WU, JS
;
LIOU, DC
BLENDS OF POLYCARBONATE AND POLYACETAL
(1991)
CHANG, FC
;
YANG, MY
;
WU, JS
;
交大名義發表
;
應用化學系
Immiscible blends of polycarbonate (PC) and polyacetal (polyoxymethylene, POM) were investigated through rheological measurements, tensile, impact, TEM, SEM, FTi.r. and thermal analysis. The large difference in melt viscosities between these two matrix polymers makes this blending system extremely difficult to process and results in partial thermal degradation of POM. The formation of a strong interpenetrating interface in PC/POM blends significantly raises tensile yield strength, modulus and heat distortion temperature above the average values for the individual polymers. Thermoplastic polyurethane elastomer is not very efficient in toughening PC/POM blends because the elastomer distributes selectively in the PC phase. The rheological morphologies of the blends are interpreted through TEM and SEM photomicrographs.
CHARACTERIZATION OF IMPROVED ALGAAS/GAAS RESONANT TUNNELING HETEROSTRUCTURE BIPOLAR-TRANSISTORS
(1991-02-01)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG
We report on the fabrication of AlGaAs/GaAs resonant tunneling heterostructure bipolar transistors (RTHBT's). The devices exhibit a current peak in the transfer characteristics, with peak-to-valley current ratios of 1.7 and 9 at 300 K and 77 K, respectively. The common-emitter small signal current gains at 300 K and 77 K reach 40 and 28, respectively. They are the best results to date for AlGaAs/GaAs resonant tunneling transistors. Because the double barriers are placed in the emitter and far from the emitter-base interface, and the heterostructure emitter suppresses the hole injection from the base to the emitter, the occurrence of the negative differential resistance (NDR) in the device characteristics is governed by the emitter current but not by the base current. The operation mechanism of the NDR behavior in the common-emitter output characteristics is discussed.
DELTA-DOPED QUANTUM-WELL STRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY
(1990-10-29)
LIU, DG
;
LEE, CP
;
CHANG, KH
;
WU, JS
;
LIOU, DC
EFFECT OF POLARIZATION MODE DISPERSION ON A COHERENT OPTICAL-SYSTEM WITH PILOT CARRIER
(1993-02-01)
KAO, MS
;
WU, JS
;
電信工程研究所
;
Institute of Communications Engineering
The effect of fiber polarization mode dispersion (PMD) on a coherent optical system with pilot carrier is twofold. First, the PMD causes state of polarization (SOP) mismatch between the message signal and pilot carrier. Second, the degrees of polarization (DOP) of the message signal and pilot carrier are degraded by PMD. Because coherent reception relies both on the SOP's and DOP's of the waves, system performance is degraded by PMD. The effect of SOP mismatch causes intermediate frequency (IF) signal amplitude degradation whereas DOP variation not only results in IF signal amplitude degradation but further induces IF noises. Here we derive analytical expressions to evaluate the performance degradation. It is shown that there is no performance degradation if only one principle state of polarization is excited and maximum degradation occurs when both principle states of polarization are equally excited. We also find that significant degradation may happen when large differential group delay exists.
EFFECT OF POLYCARBONATE MOLECULAR-WEIGHT ON POLYMER BLENDS OF POLYCARBONATE AND ABS
(1993-11-20)
WU, JS
;
SHEN, SC
;
CHANG, FC
;
交大名義發表
;
應用化學系
The melt viscosity of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends relative to PC is significantly lower, even lower than that of pure ABS in some compositions. Annealing above the T(g) of PC coalesces and coarsens phase structure in core and skin regions. Increase in the molecular weight of PC in PC/ABS blends results in low-temperature fracture toughness improvement but suffers from the disadvantage of higher melt viscosity. The selection of PC in PC/ABS blends must be a compromise between the toughness advantages of higher PC molecular weight and the disadvantages of higher melt viscosity. (C) 1993 John Wiley & Sons, Inc.
EFFECT OF RUBBER CONTENT IN ACRYLONITRILE-BUTADIENE-STYRENE AND ADDITIONAL RUBBER ON THE POLYMER BLENDS OF POLYCARBONATE AND ACRYLONITRILE-BUTADIENE-STYRENE
(1994)
WU, JS
;
SHEN, SC
;
CHANG, FC
;
交大名義發表
;
應用化學系
Higher ABS rubber content in the polycarbonate (PC)/acrynitrile-butadiene-styrene (ABS) blend resulted in toughness improvement in terms of tensile, Izod impact and strain energy release rate at a cost of higher melt viscosity. The extra-added core-shell rubber particles with poly(methyl methacrylate) (PMMA) or acrylonitrile-styrene (SAN) outer shell resided mainly in the ABS phase and further improved the resulted blends toughness. The addition of styrene-maleic anhydride (SMA) copolymer in the PC/ABS blends caused severe coagulation of the rubber particles in the ABS phase and left a greater fraction of the SAN phase without presence of rubber. The toughness improvement by increasing rubber content must be compensated by the increase of melt viscosity and this fact has to be taken into consideration in selecting the starting materials of the PC/ABS blends.
EFFICIENT ALGORITHM FOR RELIABILITY OF A CIRCULAR CONSECUTIVE-K-OUT-OF-N-F SYSTEM
(1993-03-01)
WU, JS
;
CHEN, RJ
;
交大名義發表
;
資訊工程學系
;
National Chiao Tung University
The time complexities of previously published algorithms for circular consecutive-k-out-of-n:F system are O(n . k2) and O(n . k). This paper proposes a method to improve upon the original O(n . k2) algorithm and hence derives an O(n . k) algorithm.
EFFICIENT ALGORITHMS FOR K-OUT-OF-N AND CONSECUTIVE-WEIGHTED-K-OUT-OF-N-F SYSTEM
(1994-12-01)
WU, JS
;
CHEN, RJ
;
資訊工程學系
;
Department of Computer Science
A new reliability model, consecutive-weighted-k-out-of-n:F system, is proposed and an O(n) algorithm is provided to evaluate its reliability. An O(n.min(n,k)) algorithm is also presented for the circular case of this model. We design an O(n) parallel algorithm using k processors to compute the reliability of k-out-of-n systems, that achieves linear speedup.
ELECTRICAL CHARACTERISTICS OF DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES WITH DIFFERENT ELECTRODE DOPING CONCENTRATIONS
(1991-04-01)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG
The electrical characteristics of AlGaAs/GaAs double-barrier resonant tunneling structures with various electrode doping concentrations have been studied. It was found that the peak current and the valley current are not sensitive to the change in the doping level of the electrodes. The peak-current voltage and the valley-current voltage, however, increase when the electrode doping level is lowered. These behaviors are explained using the band-bending effect in the electrodes. For devices with lightly doped or undoped electrodes, the quantum size effect in the accumulation layer due to the strong band bending causes additional kinks in the current-voltage characteristics. They are attributed to the resonant tunneling of electrons from the quantized levels in the accumulation layer. The quantum effect also accounts for the improved negative differential resistance behavior.
EXTENDING TRANSMISSION DISTANCE OF HIGH-DENSITY WDM SYSTEMS USING POST TRANSMITTER FIBER RAMAN AMPLIFIERS
(1991-03-01)
KAO, MS
;
WU, JS
;
電信工程研究所
;
Institute of Communications Engineering
We investigate the behavior of the multichannel signals in a high-density WDM system with the consideration of stimulated Raman scattering. We provide a parameter to evaluate the depth of Raman crosstalk and analyze the transmission distance limitation imposed by Raman crosstalk. To extend the system transmission distance, a post transmitter fiber Raman amplifier is employed. The allocation of signal channels on the pump gain profile is discussed. We found that there exists an optimum pump power which results in a maximum amplifier gain. The example shows that the transmission distance limitation imposed by Raman crosstalk can be extended by 20 km for a 30-channel system with 0.25-dB/km fiber loss.
FRACTURE AND IMPACT PROPERTIES OF POLYCARBONATES AND MBS ELASTOMER-MODIFIED POLYCARBONATES
(1992-01-25)
CHANG, FC
;
WU, JS
;
CHU, LH
;
交大名義發表
;
應用化學系
Mechanical properties of polycarbonates (PCs) and elastomer-modified polycarbonates with various molecular weights (MW) are investigated. Higher MW PCs show slightly lower density, yield stress, and modulus. The ductile-brittle transition temperature (DBTT) of the notched impact strength decreases with the increase of PC MW and with the increase of elastomer content. The elastomer-modified PC has higher impact strength than does the unmodified counterpart if the failure is in the brittle mode, but has lower impact strength if the failure is in the ductile mode. The critical strain energy release rate (G(c)) measured at -30-degrees-C decreases with the decrease of PC MW. The extrapolated zero fracture energy was found at M(n) = 6800 or MFR = 135. The G(c) of the elastomer-modified PC (MFR = 15, 5% elastomer) is about twice that of the unmodified one. The presence of elastomer in the PC matrix promotes the plane-strain localized shear yielding to greater extents and thus increases the impact strength and G(c) in a typically brittle fracture. Two separate modes, localized and mass shear yielding, work simultaneously in the elastomer-toughening mechanism. The plane-strain localized shear yielding dominates the toughening mechanism at lower temperatures and brittle failure, while the plane-stress mass shear yielding dominates at higher temperatures and ductile failure. For the elastomer-modified PC (10% elastomer), the estimated extension ratio of the yielding zone of the fractured surface is 2 for the ductile failure and 5 for the brittle crack. A criterion for shifting from brittle to ductile failure based on precrack critical plastic-zone volume is proposed.
HIGH-QUALITY ALGAAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY AT LOW-TEMPERATURES
(1992-03-01)
CHANG, KH
;
WU, JS
;
LIU, DG
;
LIOU, DC
;
LEE, CP
Low-temperature (approximately 600-degrees-C) molecular beam epitaxy (MBE) growth of AlGaAs has been studied. It was found that the quality of AlGaAs grown at low temperatures can be as good as that grown at high temperatures ( > 700-degrees-C) if the source materials and the growth chamber are very clean. The threshold currents of Al0.6Ga0.4As/Al0.15Ga0.85As/Al0.6Ga0.4As double heterostructure (DH) lasers grown at low temperatures and high temperatures are almost the same. The material quality can be further improved with a proper amount of indium doping. Photoluminescence (PL) linewidths of 3.1 meV and 1.7 meV have been measured for In-doped Al0.42Ga0.58As and Al0.18Ga0.82As at 4 K, respectively. They are the narrowest linewidths for the MBE-grown AlGaAs with comparable Al contents at any growth temperature. With a proper amount of In doping, double-barrier resonant tunnelling diodes have also shown improved peak-to-valley current ratios.
IMPROVED ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES USING 2-DIMENSIONAL SOURCE ELECTRONS
(1991-01-15)
WU, JS
;
LEE, CP
;
CHANG, CY
;
CHANG, KH
;
LIU, DG
We report the enhancement of peak-to-valley current ratios (PVCRs) of double-barrier resonant tunneling structures (DBRTSs) based on the AlGaAs/GaAs material system. The PVCRs as high as 25.4 and 18 have been obtained at 77 K for superlattice and alloy barrier structures with 0.2-mu-m undoped electrodes, respectively. These are the largest PVCRs to date for AlGaAs/GaAs DBRTSs. The large band bending across the undoped electrodes causes size quantization of the accumulation layer, resulting in better resonant tunneling characteristics.
INFLUENCE OF INDIUM DOPING ON ALGAAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY
(1990-10-15)
CHANG, KH
;
LEE, CP
;
WU, JS
;
LIU, DG
;
LIOU, DC
INTRINSIC AND EXTRINSIC EFFECTS ON PERFORMANCE LIMITATION OF ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES
(1992-05-01)
WU, JS
;
LEE, CP
;
CHANG, CY
;
CHANG, KH
;
LIU, DG
The performance limitations of negative differential resistance (NDR) in AlGaAs/GaAs double-barrier resonant tunneling structures (DBRTSs) have been investigated by varying the barrier thickness and quantum well (QW) width, and by doping In into the barrier layers. For devices with thick barriers (greater-than-or-equal-to 70 angstrom), the scattering in the material is believed to cause the saturation of the peak-to-valley current ratio (PVCR). The dependence of PVCR on the well width, however, is found to be, to the first-order, not related to the scattering mechanisms or other material properties. It is rather an inherent property of the tunneling process under different conditions. On the other hand, it was found that a proper amount of In doping into the barrier layers can increase the PVCR, because of the lower defect concentration, resulting in lower scattering rate in the active region.